Tree Swallow pair during the incubation phase. I would speculate that the female is setting on eggs and her mate comes to relieve her so she can get a bite to eat. It’s fairly common that I don’t see a bird peering out, but once she does it can be minutes before the male shows up and the female flies off.
I often consider what the birds might be thinking when I capture such an action series. Rather than share what I have on my mind, I’ve decided to offer you the chance to contemplate the avian exchange for yourself! If you are so inclined, feel free to share in the comments section!